JP2002110157A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a good nonaqueous electrolyte secondary battery with high capacity and high efficient charge and discharge characteristic by providing a negative pole whose battery capacity is large and whose high efficient charge and discharge characteristic is not declined. SOLUTION: This nonaqueous electrolyte battery utilizes material which is enabled to insert and desorb lithium ion to a positive pole as well as utilizing graphite to a negative pole, and is provided with a nonaqueous electrolyte composed of solute and organic solvent. The graphite utilized in the negative pole contains at least crystallite of hexagonal crystal structure and crystallite of rhombohedron structure. Peak intensity ratio (P1/P2) of peak intensity (P1: diffraction angle 43.2 deg.±0.5 deg.) of (101) plane by an X ray diffractometry utilizing a Cu-Kα line source of the rhombohedron structure and the peak intensity (P2: diffraction angle 44.3 deg.±0.5 deg.) of the (101) plane by the X ray diffractometry utilizing the Cu-Kα line source of the hexagonal crystal structure is optimized to be >=0.20 and <=0.30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a negative electrode comprising graphite (however,
The (002) plane spacing (d ₀₀₂ ) is 0.3380 nm or less, and the crystallite size (Lc) in the c-axis direction is 15 n.
m) or more, a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution in which a positive electrode is made of a material capable of inserting and extracting lithium ions, and a solute comprising a lithium salt is dissolved in an organic solvent. In particular, it relates to improvement of a negative electrode.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have come into practical use as small, lightweight, high-capacity, chargeable / dischargeable batteries, and portable electronic and communication equipment such as small video cameras, mobile phones, and notebook computers. And so on.
This type of lithium secondary battery uses a carbon-based material capable of inserting and extracting lithium ions as a negative electrode active material, and uses LiCoO ₂ , LiNiO ₂ , and LiMn as a positive electrode active material.
_This is a secondary battery including a lithium-containing transition metal oxide such as ₂ O ₄ and LiFeO ₂ and a non-aqueous electrolyte in which a solute composed of a lithium salt is dissolved in an organic solvent.

[0003] Meanwhile, carbon-based materials used for the negative electrode of such a lithium secondary battery have attracted attention because they have little capacity deterioration during charge / discharge cycles and have excellent durability. This is because the carbon-based material is capable of reversibly inserting and extracting lithium at a low potential, and utilizes the reversible formation of an intercalation compound between lithium and the carbon-based material. . For example, a positive electrode containing a sufficient amount of lithium and a carbon-based material as a negative electrode are inserted into a battery can with a separator interposed therebetween, and a non-aqueous solution in which a solute composed of a lithium salt is dissolved in an organic solvent is added thereto. By injecting the electrolyte, the battery is completely assembled in a discharged state.

[0004] When the battery is charged in the first cycle, lithium in the positive electrode is electrochemically doped between the layers of the negative electrode carbon-based material, and when the battery is discharged, the doped lithium becomes negative electrode carbon. Undoped from between layers of material,
It returns to the inside of the positive electrode again. In this case, the discharge capacity per unit mass (mAh / g) of the carbon-based material is determined by the capacity capable of occluding and releasing lithium. Therefore, in such a negative electrode, the electrochemically reversible storage amount of lithium is made as large as possible. It is desirable to do. When an intercalation compound of lithium and carbon is electrochemically generated in a battery, theoretically, the state of occlusion at a ratio of one lithium atom to six carbon atoms is an upper limit, and lithium and carbon-based compounds are theoretically formed. The interlayer compound becomes saturated with the material.

[0005]

The carbon-based materials satisfying the above conditions include naturally occurring natural graphite, artificial graphite obtained by graphitizing coke, and artificial graphite obtained by graphitizing an organic polymer or a composite thereof. Studies have been made on graphite, artificial graphite in which pitch is graphitized, and the like. These graphite materials have attracted particular attention because they have a large amount of occlusion / release of lithium and have a low and flat operating potential over the entire region.

Since the battery capacity is related to how much active material is filled in a limited battery can, the capacity per unit volume of the active material, in other words, the packing density of the carbon-based material is reduced. It is important how much you do. Therefore,
Obtaining a carbon electrode densely filled with natural graphite with developed graphite crystals or artificial graphite obtained by graphitizing coke, and producing a lithium secondary battery using this carbon electrode, it is clear that a battery with a large capacity However, on the other hand, there was a problem that the high-rate charge / discharge characteristics deteriorated.

[0007] Then, when the cause of the deterioration of the high-rate charge / discharge characteristics was pursued, the following knowledge was obtained. That is, it was revealed that natural graphite in which graphite crystals are developed or artificial graphite obtained by graphitizing coke has crystallites having a rhombohedral structure and crystallites having a hexagonal structure. Then, it was found that when graphite having many crystallites having a rhombohedral structure was used, the discharge capacity increased, but the high-rate discharge characteristics deteriorated. On the other hand, it has been found that the use of graphite having a small number of crystallites having a rhombohedral structure reduces the discharge capacity but improves the high-rate discharge characteristics. The present invention has been made on the basis of the above-described findings, and a specific graphite is filled at a high density to obtain a negative electrode having a large battery capacity and a high-rate charge / discharge characteristic which is not deteriorated. An object is to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics.

[0008]

In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode comprising graphite (provided that the (002) plane spacing (d ₀₀₂ ) Is 0.3380 nm or less, and the crystallite size (Lc) in the c-axis direction is 15 nm or more), a material capable of inserting and removing lithium ions is used for the positive electrode, and a lithium salt is used as the organic solvent. A non-aqueous electrolyte in which a solute is dissolved. The graphite used for the negative electrode has at least a hexagonal crystallite and a rhombohedral crystallite, and has a rhombohedral crystallite Cu-
The peak intensity of the (101) plane by X-ray diffraction using a Kα source (P1: diffraction angle 43.2 ° ± 0.5 °) and a Cu—Kα source having hexagonal crystallites were used. Peak intensity of (101) plane by X-ray diffraction method (P2: diffraction angle 44.3)
° ± 0.5 °) and the peak intensity ratio (P1 / P2) is 0.
It is optimized so that it is not less than 20 and not more than 0.30.
It should be noted that the peak intensities P1 and P2 in the present invention refer to FIGS.
The height from the background line (dotted line in each figure) to the peak at each diffraction angle in the X-ray diffraction diagrams shown in FIGS. 4 and 9 is shown.

When graphite having a hexagonal crystallite and a rhombohedral crystallite is used for the negative electrode, the peak intensity of the rhombohedral crystallite (P1: diffraction angle 43.2 ° ± 0.
5 °) and the peak intensity ratio of the peak intensity of the crystallite having a hexagonal structure (P2: diffraction angle 44.3 ° ± 0.5 °) (P1 / 1).
When P2) is less than 0.20, the discharge capacity is reduced even at a low load, and the peak intensity ratio (P1 / P2) is not greater than 0.20.
When it is larger than 30, the result that the capacity decrease significantly increases under a high load was obtained.

From these experimental results, it is found that high capacity can be achieved by using graphite having the above peak intensity ratio of 0.20 or more for the negative electrode, and conversely, graphite having the above peak intensity ratio of 0.30 or less can be used as the negative electrode. It is thought that the lithium ion insertion / desorption reaction smoothly proceeds even under high-density packing, and the capacity does not decrease even under a high load. Therefore, in order to obtain a negative electrode having high capacity and excellent high-rate discharge characteristics, the peak intensity of crystallites having a rhombohedral structure (P1: diffraction angle 4
3.2 ° ± 0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity of the crystallite having a hexagonal structure (P2: diffraction angle 44.3 ° ± 0.5 °) is 0.20. It is necessary to optimize so as to be 0.30 or less.

Further, the peak intensity ratio (P1 / P2) is
Even if it is not in the range, two or more types of graphite with different crystallinity
The peak intensity ratio can be
(P1 / P2) is 0.20 or more and 0.30 or less
The same effect as above can be achieved by mixing and preparing
Swell. And the filling density of graphite is 1.60 g / cm.
^ThreeIf less than, the peak intensity ratio of the crystallite (P1 / P2)
Is optimized to less than 0.20 and less than 0.30
The effect of improving the electric capacity and discharge capacity ratio, that is,
It is difficult to achieve the effect of capacity reduction even under high load
Therefore, the peak intensity ratio of the crystallite used for the graphite negative electrode (P1
/ P2) to optimize from 0.20 to 0.30
In this case, the packing density of graphite is 1.60 g / cm.^ThreeHigher than
It is desirable to perform density filling.

The present invention can be used without any limitation on the type of positive electrode active material, non-aqueous electrolyte, separator, and the like. For example, as a positive electrode active material,
A metal oxide containing at least one kind of manganese, cobalt, nickel, vanadium, and niobium, specifically, a composition formula of Li _a MO _b (M is one kind selected from Mn, Co, Ni, V, Nb, etc.) A metal element, 0 ≦ a ≦ 2 and 1 ≦ b ≦
The composite oxide of the metal M and Li represented by 5) can be used. For example, LiMn ₂ O ₄ , LiCoO ₂ , L
iNiO ₂ , LiMn _1.5 Ni _0.5 O _{4 and the} like are preferable.

Examples of the solvent for the non-aqueous electrolyte include dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, -Methyl-1,3-oxazolidin-2-one, γ-butyrolactone, diethyl carbonate, butyl methyl carbonate, ethyl propyl carbonate,
Butyl ethyl carbonate, dipropyl carbonate,
1,2-dimethoxyethane, tetrahydrofuran, 2-
A simple substance such as methyltetrahydrofuran, 1,3-dioxolan, methyl acetate, and ethyl acetate, a two-component mixture, a three-component mixture, or the like is used. The solutes dissolved in these solvents include LiPF ₆ , LiBF ₄ , Li
CF ₃ SO ₃ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , L
iC (CF ₃ SO ₂ ) ₃ , LiCF ₃ (CF ₂ ) ₃ SO _{3 and the} like are used.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the nonaqueous electrolyte battery according to the present invention will be described below. 1. Raw material graphite powder The spacing (d ₀₀₂ ) between (002) faces is 0.3363 nm
Then, massive graphite (artificial graphite fired at 2950 ° C.) having a crystallite size (Lc) of 90 nm in the c-axis direction and an average particle diameter of 20 μm was prepared, and this was designated as graphite powder α. Also,
(002) plane spacing (d ₀₀₂ ) is 0.3370 nm
Then, massive graphite (artificial graphite fired at 2800 ° C.) having a crystallite size (Lc) of 60 nm in the c-axis direction and an average particle diameter of 20 μm was prepared, and this was designated as graphite powder β.

The spacing (d ₀₀₂ ) of the (002) plane is 0.3380 nm, and the crystallite size (L
c) a massive graphite (26) having a diameter of 40 nm and an average particle diameter of 20 μm;
An artificial graphite fired at 50 ° C.) was prepared and used as graphite powder γ. Further, the plane spacing (d ₀₀₂ ) of the (002) plane is 0.3357 nm, and the crystallite size (L
c) Lumpy graphite (natural graphite) having a 200 nm average particle diameter of 20 μm was prepared and used as graphite powder δ.

2. Fabrication of Monopolar Cell (1) Fabrication of Negative Electrode Next, each of the graphite powders α, β, γ,
Each of these graphite powders α, β, γ, δ
A dispersion of styrene-butadiene rubber (SBR) (solid content: 48% by mass) was dispersed in water, and carboxymethylcellulose (CMC) as a thickener was added and mixed to prepare slurries. In addition, the mass composition ratio after drying of massive graphite, SBR, and CMC was adjusted so that massive graphite: SBR: CMC = 95: 3: 2.

Next, a negative electrode current collector made of a copper foil was prepared, and the respective slurries prepared as described above were applied to both surfaces of the negative electrode current collector by a doctor blade method, and a graphite material layer (thickness: 80 μm) was formed. The surface area is 8cm
² ). Thereafter, the graphite material was rolled so as to have a packing density of 1.60 g / cm ^3, and vacuum-dried at 100 ° C. for 2 hours to produce graphite negative electrodes. A graphite negative electrode using graphite powder α was used as a negative electrode a, a graphite negative electrode using graphite powder β was used as a negative electrode b, a graphite negative electrode using graphite powder γ was used as a negative electrode c, and a graphite negative electrode using graphite powder δ was used. A negative electrode d was obtained.

(2) Measurement of Peak Intensity Ratio After the graphite layers were separated from the graphite negative electrodes a, b, c, and d prepared as described above, the separated graphite layers were separated by a Cu-Kα radiation source. As a result of X-ray diffraction by the used X-ray diffractometer, X-ray diffraction as shown in FIG. 1 (graphite negative electrode a), FIG. 2 (graphite negative electrode b), FIG. 3 (graphite negative electrode c) and FIG. A line diffraction pattern was obtained. Next, based on these diffraction patterns, the peak intensity (cps) P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ± 0.5 °)
And the peak intensity ratio (P1 / P2) between the peak intensity (cps) P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having a hexagonal structure is calculated as follows. The result was as shown in FIG. In addition, each peak intensity P1, P2
Represents the height from the background line (dotted line in each figure) to the peak at each diffraction angle in the X-ray diffraction diagrams of FIGS.

(3) Manufacture of monopolar cell Using the graphite negative electrodes a, b, c and d manufactured as described above,
A solution prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 50 to 50 was used as an organic electrolyte, and a polypropylene microporous membrane was formed. Three-electrode single-electrode cells A, B, C, and D were produced using lithium metal plates as a separator, a counter electrode of each of the graphite negative electrodes a, b, c, and d and a reference electrode. The graphite negative electrode a
A three-electrode single-electrode cell using a graphite negative electrode b was used as a single-electrode cell A, a three-electrode single-electrode cell using a graphite negative electrode b was used as a single-electrode cell B, and a three-electrode single-electrode cell using a graphite negative electrode c was used as a single-electrode cell. The cell C was used, and a three-electrode single-electrode cell using the graphite negative electrode d was used as a single-electrode cell D.

(4) Unipolar charge / discharge test Using these unipolar cells A, B, C, and D, at room temperature (about 25 ° C.), at a current density of 0.5 mA / cm ² , constant current charging until 2.0 mV, after the current density was constant voltage charging until the 0.10mA / cm ² at 2.0 mV, at a current density of 0.5 mA / cm ^2, the battery voltage 1.0V The discharge capacity (single electrode discharge capacity) (mAh / g) per gram of the graphite material of the negative electrode was calculated from the discharge time by discharging / charging only once to obtain a result as shown in Table 1 below. Was.

[0021]

[Table 1]

From the results shown in Table 1, the peak intensity P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ±
0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having the hexagonal structure, Single electrode discharge capacity (m
Ah / g) is plotted on the vertical axis, and the results are as shown in FIG. As is clear from the results of FIG. 5, it can be seen that as the peak intensity ratio (P1 / P2) increases, the unipolar discharge capacity (mAh / g) increases. And
Since a battery having a larger capacity can be obtained by using an electrode having a larger unipolar capacity, it can be said that it is better to use graphite having a peak intensity ratio (P1 / P2) as large as possible.
Practically, if the single electrode capacity is 350 mAh / g or more,
A fairly high capacity battery is obtained. Therefore, it can be said that the peak intensity ratio (P1 / P2) is preferably set to 0.20 or more.

3. Non-Aqueous Electrolyte Secondary Battery (1) Preparation of Negative Electrode Then, each of the graphite powders α, β, δ prepared as described above was used, and these graphite powders α, β, δ were used as binders. A dispersion (solid content: 48% by mass) with styrene-butadiene rubber (SBR) is dispersed in water, and then carboxymethyl cellulose (CM) serving as a thickener is dispersed.
C) was added and mixed to prepare respective slurries. In addition, the mass composition ratio after drying of massive graphite, SBR, and CMC was adjusted so that massive graphite: SBR: CMC = 95: 3: 2.

As the binder, instead of styrene-butadiene rubber (SBR), methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) Ethylenically unsaturated carboxylic acid esters such as acrylates, or acrylic acid, methacrylic acid,
Ethylenically unsaturated carboxylic acids such as itaconic acid, fumaric acid and maleic acid may be used. As a thickener, instead of carboxymethyl cellulose (CMC),
Methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein, and the like may be used.

Next, a negative electrode current collector made of a copper foil was prepared, and the slurry prepared as described above was applied to both surfaces of the negative electrode current collector at a rate of 100 g per unit area of the negative electrode current collector by a doctor blade method. / M ² respectively to form negative electrode graphite material layers. Thereafter, the graphite material is rolled to a packing density of 1.6 g / cm ³ ,
Vacuum drying was performed at 100 ° C. for 2 hours to prepare graphite negative electrodes. The graphite negative electrode using the graphite powder α was replaced with a negative electrode e.
The graphite negative electrode using the graphite powder β was defined as a negative electrode f, and the graphite negative electrode using the graphite powder δ was defined as a negative electrode g.

(2) Measurement of peak intensity ratio After exfoliating the graphite layers from the graphite negative electrodes e, f, and g prepared as described above, these exfoliated graphite layers were separated by C.
Each was X-ray diffracted by an X-ray diffractometer using a u-Kα ray source to obtain an X-ray diffraction pattern in the same manner as described above. Next, based on these diffraction diagrams, the peak intensity (cps) P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ± 0.
5 °) and the peak intensity ratio (P1 / P2) between the peak intensity (cps) P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having a hexagonal crystal structure, and The peak intensity ratio (P1 / P
When 2) was obtained, the results were as shown in Table 2 below.

(3) Preparation of positive electrode Lithium cobaltate (LiCoO ₂ ) having an average particle size of 5 μm
The powder and artificial graphite powder as a conductive agent were mixed at a mass ratio of 9: 1 to prepare a positive electrode mixture. This positive electrode mixture,
A positive electrode slurry is prepared by kneading a binder solution in which 5% by mass of polyvinylidene fluoride (PVdF) is dissolved in N-methyl-2-pyrrolidone (NMP) so as to have a solid content mass ratio of 95: 5. did. Then, a positive electrode current collector made of aluminum foil was prepared, and the positive electrode slurry prepared as described above was applied to both surfaces of the positive electrode current collector at 240 g / m ² per unit area of the positive electrode current collector by a doctor blade method. Thus, a positive electrode mixture layer was formed. Thereafter, rolling was performed so that the packing density of the positive electrode mixture became 3.2 g / cm ³ , followed by vacuum drying at 150 ° C. for 2 hours to prepare a positive electrode. In addition, LiMn ₂ O ₄ , Li was used instead of LiCoO ₂ as the positive electrode active material.
A composition formula such as NiO ₂ , LiMn _1.5 Ni _0.5 O ₄ is Li _a
Composite oxide of MO _b (M is Mn, Co, Ni, V, in one metal element selected from such Nb, 0 ≦ a ≦ 2 1 ≦ b ≦ 5) metal M and Li represented by An object may be used.

(4) Production of Lithium Secondary Battery Next, an example of producing a lithium secondary battery will be described with reference to FIG. Here, in FIG. 6, the graphite negative electrodes e, f, and g manufactured as described above are referred to as a negative electrode plate 10, and the positive electrode manufactured as described above is illustrated as a positive electrode plate 20.
Then, as shown in FIG. 6, the negative electrode plate 10 and the positive electrode plate 20 are overlapped with a separator 30 made of a microporous polyethylene film interposed therebetween, and then spirally wound to form a spiral electrode body. Was prepared. After the insulating plates 41 were arranged above and below the electrode body, the electrode body was inserted through an opening of a steel outer can 40 also serving as a negative electrode terminal formed by pressing a single plate into a cylindrical shape.

Next, the negative electrode current collecting tab 10a extending from the negative electrode plate 10 of the electrode body is welded to the inner bottom of the outer can 40, and the positive electrode current collecting tab 20a extending from the positive electrode plate 20 of the electrode body is interrupted. The bottom plate 54 of the sealing body 50 was welded.
Then, a mixed solvent (EC: DEC =) composed of ethylene carbonate (EC) and diethyl carbonate (DEC)
After injecting an organic electrolytic solution in which LiPF ₆ is dissolved at 1 mol / l in a ratio of 50: 50: volume (50: 50: volume ratio) into the outer can 40, an insulating can insulating gasket 42 made of polypropylene (PP) is inserted into the opening of the outer can 40. The current-blocking sealing body 50 is placed via the current-blocking sealing body 50,
Sealed liquid tightly to a nominal capacity of 1450 mA
h of lithium secondary batteries E, F, and G, respectively.
The lithium secondary battery using the graphite negative electrode plate e was
And a lithium secondary battery using the graphite negative electrode plate f
And a lithium secondary battery using the graphite negative electrode plate
And

The current blocking sealing body 50 is a stainless steel positive electrode cap 5 formed in an inverted dish shape (cap shape).
1 and a stainless steel bottom plate 54 formed in a dish shape. These positive electrode cap 51 and bottom plate 54
And a power lead-out plate made of aluminum foil (not shown) that is deformed when the gas pressure inside the battery rises to a predetermined pressure or more, and a PTC (Posi
tive Temperature Coefficient) is provided. Then, when an overcurrent flows in the battery and an abnormal heat generation phenomenon occurs, the resistance value of the PTC thermistor element increases to reduce the overcurrent. Further, when the gas pressure inside the battery rises and becomes equal to or higher than a predetermined pressure, the power lead-out plate is deformed, so that the contact between the power lead-out plate and the positive electrode cap 51 is cut off, so that overcurrent or short-circuit current is cut off. It has been done.

The solvent for the organic electrolyte is ethyl
Carbonate (EC) and diethyl carbonate (DE
Ethylene carbonate instead of the mixed solvent consisting of C)
G, propylene carbonate, butylene carbonate,
Vinylene carbonate, cyclopentanone, sulfora
, 3-methylsulfolane, 2,4-dimethylsulfora
3-methyl-1,3-oxazolidin-2-one;
γ-butyrolactone, dimethyl carbonate, ethyl methyl
Chill carbonate, butyl methyl carbonate, ethyl
Propyl carbonate, butyl ethyl carbonate, di
Propyl carbonate, 1,2-dimethoxyethane,
Trahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolan, methyl acetate, ethyl acetate, etc.
A simple substance, a two-component mixture or a three-component mixture may be used.
No. The solute of the organic electrolyte is LiPF₆Niyo
Oh, LiBF_Four, LiCF _ThreeSO_Three, LiAsF₆, Li
N (CF_ThreeSO_Two)_Two, LiC (CF_ThreeSO_Two)_Three, LiCF
_Three(CF_Two)_ThreeSO_ThreeOr the like may be used.

(5) Charge / discharge test of lithium secondary battery Using these batteries E, F, G, at room temperature (about 25 ° C.)
With a charging current of 1450 mA (1 C: C represents an electrode capacity and also referred to as It), a constant current charging is performed until the battery voltage reaches 4.2 V, and a current reaches 20 mA at a constant voltage of 4.2 V. After charging at a constant voltage, the battery was discharged and charged only once at a discharge current of 1450 mA (1 C) until the battery voltage reached 2.75 V, and the discharge capacity (mAh) at 1 C was determined from the discharge time. .

Using these batteries E, F, and G, a constant current charge was performed at room temperature (about 25 ° C.) at a charge current of 1450 mA (1 C) until the battery voltage reached 4.2 V.
Charge / discharge is performed only once with a constant voltage of 4.2 V and a constant voltage charge until the current value reaches 20 mA, and then with a discharge current of 3625 mA (2.5 C) until the battery voltage reaches 2.75 V. The discharge capacity at 2.5 C (high-rate discharge capacity) (mAh) was determined from the discharge time. Then
The ratio of the discharge capacity at 1C to the discharge capacity at 2.5C is calculated, and the discharge capacity ratio (discharge capacity ratio = (discharge capacity at 1C / discharge capacity at 2.5C) × 100%) is obtained. The results are as shown in Table 2 below.

[0034]

[Table 2]

From the results shown in Table 2, the peak intensity P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ±
0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having the hexagonal structure, When the discharge capacity, high rate discharge capacity and discharge capacity ratio are plotted on the vertical axis,
The result was as shown in FIG. As is clear from the results in FIG. 7, the discharge capacity at 1C (black circles in FIG. 7) is almost constant regardless of the peak intensity ratio (P1 / P2).
It can be seen that the discharge capacity at 2.5 C (open circles in FIG. 7) and the discharge capacity ratio (x marks in FIG. 7) decrease as the peak intensity ratio (P1 / P2) increases.

From the results shown in FIG. 7, the high rate discharge capacity and the discharge capacity ratio are almost constant until the peak intensity ratio (P1 / P2) is 0.30, and particularly, the peak intensity ratio (P1 / P2) is 0.30. If the peak intensity ratio (P1 / P2) is regulated to 0.30 or less, it is understood that a lithium secondary battery having a high rate discharge capacity and an excellent discharge capacity ratio can be obtained. . From the results of FIG. 5, the unipolar discharge capacity increases as the peak intensity ratio (P1 / P2) increases, and the peak intensity ratio (P1 / P2) increases to 0.20.
Considering that a battery having a large capacity can be obtained by the above, it can be said that it is preferable to optimize the peak intensity ratio (P1 / P2) to be 0.20 or more and 0.30 or less.

4. Examination of packing density of graphite negative electrode (1) Lithium secondary battery using graphite negative electrode whose packing density is 1.55 g / cm ³ Using each of the graphite powders α, β, δ prepared as described above, A dispersion (solid content: 48% by mass) of each graphite powder α, β, δ and styrene-butadiene rubber (SBR) is dispersed in water, and carboxymethyl cellulose (CMC) as a thickener is added and mixed. Thus, slurries were prepared. In addition, the mass composition ratio of lump graphite, SBR, and CMC after drying is lump graphite: SBR: C
It was prepared so that MC = 95: 3: 2.

Next, a negative electrode current collector made of a copper foil was prepared, and each slurry prepared as described above was applied to both surfaces of the negative electrode current collector by a doctor blade method at a rate of 100 g per unit area of the negative electrode current collector. / M ² respectively to form negative electrode graphite material layers. Thereafter, it was rolled so that the filling density of the graphite material became 1.55 g / cm ^3, and vacuum-dried at 100 ° C. for 2 hours, thereby producing graphite negative electrode plates. The graphite negative electrode plate using graphite powder α was referred to as negative electrode plate h, the graphite negative electrode plate using graphite powder β was referred to as negative electrode plate i, and the graphite negative electrode plate using graphite powder δ was referred to as negative electrode plate j.

Next, the graphite layers were separated from the graphite negative electrodes h, i, j prepared as described above, and the separated graphite layers were respectively subjected to X-ray diffraction using a Cu-Kα ray source. X-ray diffraction was performed to obtain an X-ray diffraction pattern in the same manner as described above. Next, based on these diffraction diagrams, the peak intensity (cps) P1 of the (101) plane of the crystallite having a rhombohedral structure is obtained.
(Diffraction angle 43.2 ° ± 0.5 °) and the peak intensity (cps) P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having a hexagonal structure were obtained. When the peak intensity ratio (P1 / P2) was determined based on the respective peak intensities P1 and P2, the results shown in Table 3 below were obtained.

Next, using each of the graphite negative electrode plates h, i, and j produced as described above, a nominal capacity of 1450 m was used in the same manner as described above.
Ah lithium secondary batteries were produced. The lithium secondary battery using the graphite negative electrode plate h was referred to as a battery H, the lithium secondary battery using the graphite negative electrode plate i was referred to as a battery I, and the lithium secondary battery using the graphite negative electrode plate j was referred to as a battery J. .
Next, in the same manner as described above, the batteries H, I, and J were charged and discharged in the same manner as described above, and the discharge capacity at 1 C (mAh) and the discharge capacity at 2.5 C (high-rate discharge) were obtained. Capacity) (mAh), and a discharge capacity ratio (discharge capacity ratio =
(Discharge capacity at 1 C / discharge capacity at 2.5 C) × 100
%) Yielded the results shown in Table 3 below.

[0041]

[Table 3]

From the results shown in Table 3, the peak intensity P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ±
0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having the hexagonal structure, When the discharge capacity at 1 C, the discharge capacity at 2.5 C, and the discharge capacity ratio are plotted on the vertical axis, the results shown in FIG. 8 are obtained. As is clear from the results of FIG. 8, the discharge capacity at 1 C (FIG.
Black circles) slightly increase as the peak intensity ratio (P1 / P2) increases, but the high-rate discharge capacity and the discharge capacity ratio are almost constant even when the peak intensity ratio (P1 / P2) increases. You can see that. From this, in a lithium secondary battery using a graphite negative electrode having a graphite filling density of 1.55 g / cm ³ and a low filling density, the peak intensity ratio (P1 / P2) of crystallites used for the graphite negative electrode was determined. 0.20 or more.
Even if it is optimized to 30 or less, it can be said that the effect of improving the high rate discharge capacity and the discharge capacity ratio is hardly exhibited.

(2) Lithium secondary battery using a graphite negative electrode having a packing density of 1.70 g / cm ³ Each of the graphite powders α, β, δ prepared as described above, and a mixed graphite powder obtained by mixing γ and δ were used. Each of these graphite powders α, β, δ and a mixed graphite powder of γ and δ,
After dispersion of styrene-butadiene rubber (SBR) (solid content: 48% by mass) was dispersed in water, carboxymethylcellulose (CMC) as a thickener was added and mixed to prepare slurries. In addition, the mass composition ratio after drying of massive graphite, SBR, and CMC was adjusted so that massive graphite: SBR: CMC = 95: 3: 2.

Next, a negative electrode current collector made of copper foil was prepared, and the slurry prepared as described above was applied to both sides of the negative electrode current collector by a doctor blade method at 110 g per unit area of the negative electrode current collector. / M ² respectively to form negative electrode graphite material layers. Thereafter, the graphite material was rolled so as to have a packing density of 1.70 g / cm ^3, and vacuum-dried at 100 ° C. for 2 hours to produce graphite negative electrode plates. The graphite negative electrode plate using graphite powder α was used as negative electrode plate k, the graphite negative electrode plate using graphite powder β was used as negative electrode plate 1, the graphite negative electrode plate using graphite powder δ was used as negative electrode plate m, and graphite powder γ was used. A negative electrode plate made of a graphite negative electrode plate using a mixed graphite powder obtained by mixing δ and δ was used as a negative electrode plate n.

Then, after separating the graphite layers from the graphite negative electrodes k, l, m, and n prepared as described above, the separated graphite layers were separated by an X-ray diffractometer using a Cu-Kα ray source. Were subjected to X-ray diffraction to obtain X-ray diffraction patterns in the same manner as described above. Next, based on these diffraction diagrams, the peak intensity (cps) P of the (101) plane of the crystallite having a rhombohedral structure is obtained.
1 (diffraction angle 43.2 ° ± 0.5 °) and the peak intensity (cps) P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having a hexagonal structure, When the peak intensity ratio (P1 / P2) was determined based on these peak intensities P1 and P2, the results shown in Table 4 below were obtained. FIG. 9 shows an X-ray diffraction diagram of the graphite negative electrode n.

Next, using each of the graphite negative electrode plates k, l, m, and n produced as described above, the nominal capacity 160
Lithium secondary batteries of 0 mAh were produced. In this case, since the capacity of each graphite negative electrode plate k, l, m, n is large, the positive electrode slurry is applied so as to be 250 g / m ² per unit area of the positive electrode current collector to form the positive electrode mixture layer. A positive electrode plate formed and rolled so that the filling density of the positive electrode mixture becomes 3.2 g / cm ³ is used. A lithium secondary battery using the graphite negative electrode plate k is referred to as a battery K, a lithium secondary battery using the graphite negative electrode plate 1 is referred to as a battery L, and a lithium secondary battery using the graphite negative electrode plate m is referred to as a battery M. A lithium secondary battery using the graphite negative electrode plate n was referred to as a battery N. Then
Using these batteries K, L, M, and N, charging and discharging are performed in the same manner as described above, and the discharge capacity at 1 C (mAh) and the discharge capacity at 2.5 C (high-rate discharge capacity) (mAh) And discharge capacity ratio (discharge capacity ratio = (discharge capacity at 1 C) /
When the discharge capacity at 2.5 C) × 100%) was obtained, the results shown in Table 4 below were obtained.

[0047]

[Table 4]

From the results shown in Table 4, the peak intensity P1 of the (101) plane of the crystallite having a rhombohedral structure (diffraction angle 43.2 ° ±.
0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having the hexagonal structure, When the discharge capacity at 1 C, the discharge capacity at 2.5 C, and the discharge capacity ratio are plotted on the vertical axis, the results shown in FIG. 10 are obtained.
As is apparent from the results in FIG. 10, the discharge capacity at 1C (black circles in FIG. 10) slightly increases as the peak intensity ratio (P1 / P2) increases, but the discharge capacity at 2.5C increases. The capacity (open circles in FIG. 10) and the discharge capacity ratio (FIG.
(X mark) decreases as the peak intensity ratio (P1 / P2) increases. In particular, when the peak intensity ratio (P1 / P2) is 0.
When it exceeds 3, it can be seen that the rate of decrease is large. Further, a graphite powder (γ) having a peak intensity ratio (P1 / P2) smaller than 0.2 and a graphite powder (δ) having a peak intensity ratio (P1 / P2) larger than 0.3 are mixed to obtain a peak intensity ratio. (P1 /
Battery N using negative electrode plate n produced using mixed graphite powder prepared so that P2) becomes 0.2 or more and 0.3 or less.
Is a graphite powder not mixed with graphite powder (α, β, δ)
It can be seen that the battery has performance comparable to that of the batteries K, L, and M using the positive electrode plate (k, l, m) manufactured using.

(3) Lithium secondary battery using a graphite negative electrode having a packing density of 1.80 g / cm ³ Using each of the graphite powders α, β, and δ prepared as described above, each of these graphite powders α , Β, δ and a dispersion of styrene-butadiene rubber (SBR) (solid content: 48% by mass) are dispersed in water, and carboxymethylcellulose (CMC) as a thickener is added and mixed, and each slurry is mixed. Was prepared. In addition, the mass composition ratio of lump graphite, SBR, and CMC after drying is lump graphite: SBR: C
It was prepared so that MC = 95: 3: 2.

Next, a negative electrode current collector made of a copper foil was prepared, and each slurry prepared as described above was applied to both surfaces of the negative electrode current collector by a doctor blade method at 115 g per unit area of the negative electrode current collector. / M ² respectively to form negative electrode graphite material layers. Thereafter, it was rolled so that the packing density of the graphite material became 1.80 g / cm ^3, and vacuum-dried at 100 ° C. for 2 hours, thereby producing graphite negative electrode plates. The graphite negative electrode plate using graphite powder α was used as negative electrode plate o, the graphite negative electrode plate using graphite powder β was used as negative electrode plate p, and the graphite negative electrode plate using graphite powder δ was used as negative electrode plate q.

Next, the graphite layers were peeled off from the graphite anodes o, p, q prepared as described above, and the peeled graphite layers were respectively separated by an X-ray diffractometer using a Cu-Kα ray source. X-ray diffraction was performed to obtain an X-ray diffraction pattern in the same manner as described above. Next, based on these diffraction diagrams, the peak intensity (cps) P1 of the (101) plane of the crystallite having a rhombohedral structure is obtained.
(Diffraction angle 43.2 ° ± 0.5 °) and the peak intensity (cps) P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having a hexagonal structure were obtained. When the peak intensity ratio (P1 / P2) was determined based on the respective peak intensities P1 and P2, the results shown in Table 5 below were obtained.

Next, using the graphite negative plates o, p, and q produced as described above, a nominal capacity of 1700 m
Ah lithium secondary batteries were produced. In this case, since the capacity of each graphite negative electrode plate o, p, q is large, the positive electrode slurry is added to the positive electrode current collector in an area of 260,000 per unit area.
g / m ² to form a positive electrode mixture layer, and a positive electrode plate rolled so that the filling density of the positive electrode mixture becomes 3.3 g / cm ³ . A lithium secondary battery using the graphite negative electrode plate o was referred to as a battery O, a lithium secondary battery using the graphite negative electrode plate p was referred to as a battery P, and a lithium secondary battery using the graphite negative electrode plate q was referred to as a battery Q. . Next, using these batteries O, P, and Q, charging and discharging are performed in the same manner as described above, and the discharge capacity at 1 C (mAh) and the discharge capacity at 2.5 C (high-rate discharge capacity) (mAh) , And a discharge capacity ratio (discharge capacity ratio = (discharge capacity at 1 C / discharge capacity at 2.5 C) × 100%) was obtained. The results shown in Table 5 below were obtained.

[0053]

[Table 5]

From the results shown in Table 5, the peak intensity P1 of the (101) plane of the crystallite having the rhombohedral structure (diffraction angle 43.2 ° ±
0.5 °) and the peak intensity ratio (P1 / P2) between the peak intensity P2 (diffraction angle 44.3 ° ± 0.5 °) of the (101) plane of the crystallite having the hexagonal structure, When the discharge capacity at 1 C, the discharge capacity at 2.5 C, and the discharge capacity ratio are plotted on the vertical axis, the results shown in FIG. 11 are obtained.
As is clear from the results of FIG. 11, the discharge capacity at 1 C slightly increases as the peak intensity ratio (P1 / P 2) increases, but the discharge capacity at 2.5 C and the discharge capacity ratio show the peak intensity ratio. It can be seen that when (P1 / P2) exceeds 0.30, it sharply decreases.

Then, FIG. 7, FIG. 8, FIG.
From each result of No. 1, the following became clear. That is, in a lithium secondary battery using a graphite negative electrode having a graphite filling density of 1.55 g / cm ³ and a low filling density, the peak intensity ratio (P1 / P2) of crystallites used for the graphite negative electrode is set to 0.1. Even if it is optimized to 20 or more and 0.30 or less, it is difficult to exhibit the effect of improving the high rate discharge capacity and the discharge capacity ratio. Therefore, the peak intensity ratio (P1 / P
In the case of optimizing 2) to 0.20 or more and 0.30 or less, it is preferable to fill graphite at a high density of 1.60 g / cm ³ or more.

The filling density of graphite is 1.60 g / cm.
^In the case of high-density filling of ³ or more, a battery having a large capacity can be obtained by setting the peak intensity ratio (P1 / P2) to 0.20 or more from the results of FIG. 5, and the results of FIGS. Considering that when the peak intensity ratio (P1 / P2) exceeds 0.30, the high-rate discharge capacity and the discharge capacity ratio decrease, the peak intensity ratio (P1 / P2) is 0.30 to 0.30 or more. It can be said that the following optimization is preferable. Also, by mixing two or more types of graphite having different crystallinities, the same effect can be obtained even if the peak intensity ratio (P1 / P2) is adjusted to be 0.2 or more and 0.3 or less.

As described above, in the present invention, the peak intensity of the (101) plane of the crystallite having a rhombohedral structure by the X-ray diffraction method using a Cu-Kα ray source (P1: diffraction angle 43.2).
° ± 0.5 °) and the peak intensity of the (101) plane of a crystallite having a hexagonal structure by an X-ray diffraction method using a Cu-Kα ray source (P2: diffraction angle 44.3 ° ± 0.5 °). ) Is optimized so that the peak intensity ratio (P1 / P2) with respect to (P1 / P2) is not less than 0.20 and not more than 0.30. For this reason, the lithium ion insertion / desorption reaction is smoothly performed even under high-capacity and high-density packing, so that a lithium secondary battery whose capacity does not decrease even under high load can be obtained. Become.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram showing the relationship between the X-ray diffraction angle (2θ) and the intensity of a graphite negative electrode a.

FIG. 2 is an X-ray diffraction diagram showing the relationship between the X-ray diffraction angle (2θ) and the intensity of a graphite negative electrode b.

FIG. 3 is an X-ray diffraction diagram showing the relationship between the X-ray diffraction angle (2θ) and the intensity of the graphite negative electrode c.

FIG. 4 is an X-ray diffraction diagram showing the relationship between the X-ray diffraction angle (2θ) and the intensity of the graphite negative electrode d.

FIG. 5 is a diagram showing a relationship between a peak intensity ratio (P1 / P2) and a unipolar discharge capacity (mAh / g).

FIG. 6 is a diagram showing a cross section of a lithium secondary battery according to one embodiment of the present invention.

FIG. 7 shows the relationship between the peak intensity ratio (P1 / P2) when the packing density of graphite is 1.60 g / cm ³ , the discharge capacity at 1C, the discharge capacity at 2.5C, and the discharge capacity ratio. FIG.

FIG. 8 shows the relationship between the peak intensity ratio (P1 / P2) when the filling density of graphite is 1.55 g / cm ³ , the discharge capacity at 1C, the discharge capacity at 2.5C, and the discharge capacity ratio. FIG.

FIG. 9 is an X-ray diffraction diagram showing the relationship between the X-ray diffraction angle (2θ) and the intensity of the graphite negative electrode n.

FIG. 10 shows the relationship between the peak intensity ratio (P1 / P2) when the packing density of graphite is 1.70 g / cm ³ , the discharge capacity at 1C, the discharge capacity at 2.5C, and the discharge capacity ratio. FIG.

FIG. 11 shows the relationship between the peak intensity ratio (P1 / P2) when the packing density of graphite is 1.80 g / cm ³ , the discharge capacity at 1C, the discharge capacity at 2.5C, and the discharge capacity ratio. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Graphite negative electrode plate, 10a ... Negative electrode current collecting tab, 20 ... Positive electrode plate, 20a ... Positive electrode current collecting tab, 30 ... Separator, 40 ...
Outer can, 41: Spacer, 42: Insulating gasket for outer can, 50: Current blocking sealing body

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masatoshi Takahashi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5H029 AJ02 AJ03 AJ05 AL07 AM02 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ17 HJ04 HJ08 HJ13 5H050 AA02 AA07 AA08 BA17 CA07 CA08 CA09 CB08 FA05 FA19 GA28 HA04 HA08 HA13

Claims (3)

[Claims] A negative electrode is made of graphite (provided that the (002) plane spacing (d ₀₀₂ ) is 0.3380 nm or less, and the crystallite size (Lc) in the c-axis direction is 15 nm or more). A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which a material capable of occluding and releasing lithium ions is used and a solute comprising a lithium salt is dissolved in an organic solvent, wherein the graphite is at least rhombohedral. A crystallite having a crystal structure and a crystallite having a hexagonal structure, and the crystallite having a rhombohedral structure is determined by an X-ray diffraction method (101).
When the peak intensity ratio (P1 / P2) between the peak intensity (P1) of the plane and the peak intensity (P2) of the (101) plane of the crystallite having the hexagonal structure determined by the X-ray diffraction method is 0.20 or more, the peak intensity ratio is 0.20. 3
Non-aqueous electrolyte secondary battery characterized by being 0 or less. 2. The negative electrode is made of graphite (provided that the (002) plane spacing (d ₀₀₂ ) is 0.3380 nm or less, and the crystallite size (Lc) in the c-axis direction is 15 nm or more). A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which a material capable of occluding and releasing lithium ions is used and a solute comprising a lithium salt is dissolved in an organic solvent, wherein the graphite is at least rhombohedral. A mixed graphite in which two or more kinds of graphites having different crystal structures each having a crystallite having a crystal structure and a crystallite having a hexagonal crystal structure are mixed, and the rhombohedral crystallite is obtained by an X-ray diffraction method (101).
When the peak intensity ratio (P1 / P2) between the peak intensity (P1) of the plane and the peak intensity (P2) of the (101) plane of the crystallite having the hexagonal structure determined by the X-ray diffraction method is 0.20 or more, the peak intensity ratio is 0.20. 3
A non-aqueous electrolyte secondary battery, which is prepared to be 0 or less. 3. The packing density of the graphite is 1.60 g / cm.
^{3. The method according} to claim 1, wherein the number is ³ or more.
3. The non-aqueous electrolyte secondary battery according to 1.